1. Field of the Invention
The present invention relates generally to batteries for spacecraft applications and, more particularly, to the design and assembly of such batteries which are economical, yet tailored to meet the power requirements of specialized spacecraft. More specifically, a very large number of small battery cells are assembled electrically in parallel into a cell module to provide a larger ampere-hour capacity and, in turn, multiple cell modules are series connected into a spacecraft battery having the required power. The invention provides for (a) three dimensional packaging of parallel cells, (b) rejecting the internal heat from such a package, and (c) providing redundant electrical fuse protection for the internal cell array. In short, the invention provides a unique methodology for utilizing mass-produced electrochemical cells in low volume applications thereby reducing production and development costs, and enables the provision of batteries with flexible capacities for specialized applications.
2. Description of the Prior Art
At the present time, spacecraft batteries are typically built with custom fabricated cells built to match the required battery ampere-hour capacity. This requires that new cell sizes be developed and manufactured as the required battery ampere-hour capacity is changed. This in turn leads to specialized high cost, low volume, production facilities due to the limited cell quantities required for spacecraft use and the number of different sizes required. In addition, high quality is difficult to achieve in such production facilities as the quantities make it difficult to implement statistical process control and many of the manufacturing steps are carried out by hand.
An alternative approach is to build batteries based on parallel arrays of smaller cells which may be commercially available, although this is not a requirement of the invention. These arrays are then connected in series to yield the required battery voltage and capacity. Difficulties with this approach are that (a) a short circuit will short out the entire parallel array, (b) such arrays are typically volumetrically inefficient due to the small height of a typical commercial cell compared with a larger custom design, and (c) if the cells are packaged in a three dimensional array for improved volumetric efficiency, waste heat cannot be efficiently removed from the interior of the cell array.
An alternative to respecifying ampere - hour cell capacity is to use a fixed capacity and DC to DC conversion. This approach, however, adds mass (the converter) and increases battery weight due to the efficiency of converter.
Additionally, it is customary for known battery systems to incorporate appropriate electronics to automatically bypass a malfunctioning cell. These electronics are costly, occupy limited space, and add to the weight of the system.
It was with knowledge of the foregoing that the present invention has been conceived and is now reduced to practice.